The linear motion guide systems employed in a diversity of machines including machine tools and so on are increasingly used in recent years in a way laying their guide rails bare to the working atmosphere from the view point of increasing spaces to be reserved for processing a workpiece and for installing required equipments, making the guide units themselves compact in construction, cost savings on installations, and so on. Thus, many of modern guide units are customized to have no dustproof means including a telescopic cover, bellows, and so on.
There are known linear motion guide systems with sealing means, which are disclosed in, for example the commonly assigned Japanese Patent Laid-Open No. H9-42284. With the prior linear motion guide system, the sealing means are installed on forward and aft ends of a slider. The sealing means are each comprised of a cassette of U-shape in transverse section, two sheets of seals installed inside the cassette, an intermediate medium held between the seals to feed lubricant, and a scraper plate secured on the outward end of the outside one of the seals. Two sheets of seals are each made U-shaped in transverse section and composed of a metal core and rubber baked on the metal core to provide lips. The interference between the seals is selected at 0.5 mm, which is somewhat larger than usual to make the dust proof performance better.
Nevertheless, the sealing means for the linear motion guide system constructed as stated earlier, because of rubber-made construction, may encounter large frictional resistance and, therefore, lubricant is indispensable to sustain durability of the sealing performance. Thus, the problem faced in the linear motion actuator recited earlier is that the control of lubricant is very tough.
A linear bearing guide system capable of wiping dusts off to keep sealing performance is known in, for example Japanese Patent Laid-Open No. H11-351252. The prior linear bearing guide system has a self-lubricating guide member, which is composed of a lip seal of usual rubber and foamed urethane rubber component secured on the outward surface of a reinforcing plate and impregnated with lubricant. The guide member is protected against lubrication failure to help maintain the durability against frictional resistance.
The linear bearing guide system constructed as stated earlier, although but befitting to continuous application of lubricant to the lip seal, has a question of lacking in sealing performance.
A dustproof construction in the linear motion guide systems is known in, for example Japanese Patent Laid-Open No. 2000-227115, which is constructed to allow a slider moving in and out along a guide track with less frictional resistance. The prior dustproof construction is comprised of a lubricant reservoir component and a scraper component. The lubricant reservoir component includes three sheets of resilient members made of foamed polyurethane having open cells or pores and impregnated with lubricant, and spacer members of metallic plates each interposed between any two adjacent resilient members to form recesses. The scraper component is mounted on the slider in a way spaced away from the guide track with leaving a slight clearance between them. The foamed polyurethane with open pores is prepared to have physical properties of tensile strength of about 30˜50 kg/cm3, percent elongation of about 300˜500% and repulsion elasticity of about 30˜60%. The foamed polyurethane is impregnated with lubricant of 30˜50 weight %.
With the dustproof construction as recited just earlier, nevertheless, the foamed resilient members comes to absorb coolants and so on so that foreign matter such as any liquids builds up gradually in the resilient members. Thus, this poses a problem that the resilient members are insufficient to dislodge the foreign matter from the linear motion guide system.
Another linear guide bearing unit is disclosed in, for example known in, Japanese Patent Laid-Open. No. 2005-337407, which is constructed to keep foreign matter against entering inside the slider to prevent premature wear and breakage. The prior linear guide bearing unit is mounted on forward and aft ends of the slider and composed of the combination of many lubricant applicators, protectors, thin resinous sealing members, side seals of steel plate baked with rubber, and felt sealing members impregnated with grease.
With the linear guide bearing unit having a plurality of sealing members stacked one on the other as stated earlier, however, large axial space would be needed for installation of many sealing members.